Thank you OpenEnergyMonitor: Octopus Daikin ASHP monitoring

TrystanLea · 25 October 2023 10:01

Zooming in on October 24th:

A:

C:

Are those overnight runs for C both DHW or is one a space heating blast? If DHW why two runs finishing at different target temperatures?

The cycling at minimum modulation & low flow temp seem to be hurting cop between 11:00 and 15:00, perhaps trying to run for a longer period there at a slightly higher flow temp and higher modulation might give better performance?

Opportunity as well for reducing pump speed a bit?

I will check with my father in law what his current control settings are.

matt-drummer · 25 October 2023 13:33

As noted by Vinny yesterday DHW performance is poor.

It seems to be deteriorating!

At this level of performance I may as well use an immersion heater

I have noticed in the last couple of days that I am getting a massive spike in heat production, nearly 19kW of heat, at the end of the DHW cycle. Then I hear some nose in the radiator I am sitting next to and the radiator gets really hot at the top for a minute or so.

Timbones · 25 October 2023 13:54

I wonder if heat pump is performing just fine but there may be an issue with the heat metering. The temperatures are rising and heating up the tank in a reasonable time, but the readings seem a little noisier than I’d expect.

How are the temperature sensors connected to the pipes?
Where are the temperature sensors connected?
Where is the flow meter installed in relation to the pipework?
Do you have any other measurements, like tank temperature?

matt-drummer · 25 October 2023 14:02

Hi Tim,

I posted pictures of the heat meter installation in this topic yesterday, you should be able to see them.

The tank is heating to 45c.

I just checked DHW performance after I installed the heat meter and it was 2+

I have not experienced any unusual noises or heating of the radiators until a couple of days ago, I have been sat here whilst the DHW cycle completes many times.

I also started experiencing something else weird yesterday, I was going to post about it but didn’t. I have been watching this a lot and I haven’t seen this until yesterday.

I see the COP for the last 30 minutes at the top left of the window drop to something unbelievable but when I isolate that 30 minutes I see a realistic COP, something like 1.2 for 30 minutes but 3.8 for COP in window.

I have been thinking about blocked filters, they were cleaned in July three weeks after the install but I would have expected to see flow rate problems?

Timbones · 25 October 2023 14:38

What temperature is the tank heating from? COP is best when tank starts from cold. Need to be wary of starting temps when comparing DHW runs, as they may not be as equivalent as you think.

The start of today’s run @ 14:10, the return goes way higher than flow, suggesting that it was taking (borrowing) heat from the cylinder before the heat pump started up. The measured heat is negative for the first couple minutes as a result.

This morning’s DHW cycle @ 8:20 faired much better, yielding a COP of 3.94, which is pretty decent, though mostly thanks the slug of free heat at the end (though that may have gone to your radiators). Even the middle section averages a COP of 3, which is still good. I’d guess that the tank was colder this time.

That second DHW reheat in the afternoon was probably unnecessary, and could have been skipped entirely. Try increasing the threshold for how much the tank temperature can drop before it will reheat it (I’ve mine set to 20 degrees).

matt-drummer · 25 October 2023 14:58

Thanks Tim,

Good spot.

The DHW is set on a schedule at 14.00 every day to heat to 45c.

It is also on reheat with a hysteresis of 8c from 43c, so it reheats at 35c I think.

This is how it was set by Octopus.

Maybe I should try setting to to reheat only and abandon the scheduled heat?

Timbones · 25 October 2023 15:17

If you’re on a TOU tariff, you might be better off using only scheduled heat, but try experimenting to see what works best for you. If your heat pump allows it, then a combined approach may be better, i.e. reheat once a day but only if tank is below a certain temperature. I don’t know if this is possible with Daikin.

matt-drummer · 25 October 2023 15:24

Any scheduling is going to result in a problem like I have seen today if combined with any reheating as far as I can see.

I am on Cosy Octopus at the moment but I also have a lot of battery storage so I care less. It would be better to heat in one of the two lower priced windows.

But if I stick with my 14.00 daily schedule and it reheats at 11.00 tomorrow then it will do exactly what it has done today.

Timbones · 25 October 2023 15:25

Can you turn off the automatic reheat, so it only heats at 14:00? (I’m also on Cosy, so I do this)

matt-drummer · 25 October 2023 15:32

I can, but my wife may not be happy.

She wants a shower or to wash her hair at varying times, if I stick with a schedule I think we will run out at times.

What I could do is turn off the reheat and stick with the 14.00 schedule (I charge my batteries here too) and up the tank temperature from 45c to say 50c. That would probably ensure we have what we have now without the efficiency problems.

ColinS · 25 October 2023 17:27

I’m Trystan’s father in law and the owner of system A above so thought I would add a few findings related to the above posts. My 11.6kw Altherma Monobloc has been in for 13 months and I have been optimizing it constantly since the install. In common with many above comments while my install was good the set up/programming left by the installers was useless. Luckily I have another 8 yr old Daikin split system installed elsewhere so I have taught myself how to program these units.

DHW - COP is poor with a low tank temperature rise. Plotting kWh into the tank vs temp rise of the tank shows a flattish line kWh vs tank dT. Conclusion - as Matt has found - except when it is very cold use ‘Reheat only’ and set the reheat hysterisis about 10c (eco temp 44 and you still get warm enough water down to 34). When it is very cold (below 5c outside) then you do not want house heating to be interrupted randomly so go to Schedule (only) with DHW coming on at circa 1pm when the ambient temp usually peaks and COP will be best.
Like Matt I have found that the WD curve is not helping me as a) 37c flow temp gives me a COP of around 5 (outside = 10-12c) and 32c gives me a COP of 4. Possibly due to much lower radiator efficiency at the lower flow also b) when the ambient is below 4c and defrosting starts to bite big time into the average output a higher flow temp of say 40c might make the unit frost up faster. So I am sticking with 37c fixed with just 1degree of modulation. I should add that I am using room temp control 17c night, 19c most of the day and 21c evenings. The 17c switches it off at night except for very cold nights
Defrost is a serious output limiter for these and I suspect many other UK installed heatpumps. Last winter my 11.6kW unit struggled to average much over 7.5kW when the ambient was below 4c. My house needs 9.9kW at -2c so I needed supplemental heat for a few days. Had I installed a 16kw I suspect it would not have changed this 7.5 kw as the evaporator sizes are much the same across the 9 to 16kW range. As you need the max output at the lowest ambients I cannot see the point in building a range of units like this. As mentioned above I am hoping that a lower target flow temp of 37c max will improve the COP at lowest temps and tweak the output a little higher with longer times between defrosts. But then isn’t the amount of heat drawn out of the outside air related (proportional??) to the moisture frozen out of that air - so it might not work.
I’ve experimented with a range of flow-return dTs from 4 to 10c and optimised at 6c for my system. The HPCs achieve this easily with the fans on low. I did not see any COP gain from 4c or 5c dT.
I had serious pump/pipe/rad valve noise issues at highest flows (I only have the one pump on the ASHP) so have limited the pump to 70% which is OK. This works well as my max flow x 6c dT x specific heat = my design output at design temp (around 10kW)

Overall I’m happy with the SCOP I have been getting and am hopeful that I can tweak it higher from now on.
Hope this helps

matt-drummer · 25 October 2023 18:02

Hi Colin,

Thank you for your input, it’s really useful.

I have been so focussed on my heating that I had taken my eye off the ball with regards to DHW.

Thanks to Tim and Vinny I think I have this sorted now.

Before my heat loss survey I fully expected to have to change/move most of my radiators.

I was surprised when they only wanted to change the two obvious ones.

I had done my own radiator schedule and that is what I now plan to go with.

I feel that an oversized heat pump and radiators that are too small is compromising the performance.

There are `flashes of brilliance’ that I think I can replicate if I make changes.

I am going to significantly increase my radiator output and also increase my heat loss by adding a semi outdoor poorly insulated building.

We’ll see how it goes.

It says you have a 9kW Daikin but your post suggests otherwise?

ColinS · 25 October 2023 19:08

Sorry it’s a 10.6kW not 11.6kW unit.
I think you are right about your radiators - the saw tooth pattern in your flow temp suggest you are radiator limited. ie at the lowest compressor setting, the rads cannot stop the flow temp rising above it’s set point plus the overshoot factor…so the HP has to switch off before it reaches an equilibrium. Have you tried raising the flow temp a lot to see if you can get to an equilibrium flow temp and square wave pattern, as the higher flow temp will, eventually, raise the rad output to match the minimum compressor output x COP?

You could then back calculate the rad sizing increase you need to run steadily at a lower flow temp. I think that Rad output = K x (T rad-T room)^1.4. …although my memory might be wrong on this I’m sure others more expert than me can correct this.

I realised this when comparing my systems poorer COP last April with today. Last April the combination of lower flow temp and me setting the ‘TRVs’ on my fan units too low meant that my rad output was too low - hence saw tooth pattern like yours and lower COP.

One big plus of the Daikins is their control system - they seem to turn down progressively as the room temp is reached and modulate flow well to find their equilibrium (even if flow temp modulation is off).

Good luck!

ColinS · 25 October 2023 19:13

Not sure If I have done this correctly but first graph is end of March second is now.

matt-drummer · 25 October 2023 19:37

I tried running higher flow temperatures with pure weather compensation which may well be ok for efficiency.

The problem is that it is like an uncontrolled nuclear reaction in slow motion! The temperature of the house just runs away and increases and increases. The heat loss of the house is lower than the minimum output of the heat pump at those outdoor temperatures.

And that really is my problem concerning efficiency. The heat pump heats the house well and the electricity consumption is nothing to get alarmed about.

My conclusion is that my heat pump is too big, my heat loss is too low and my radiators are too small for the heat pump.

So I could buy a smaller heat pump, which was tempting for a while.

Live with what I have.

Or increase my radiator sizes and increase the heat loss., which is what I intend to do.

That should mean I end up with everything about right.

And the added heat loss is not important so if needs be I can cut that off to have heat for the house if really needed.

I more than half expected the radiators were not right and I was always sure that the heat pump was too big. Despite my ignorance displayed at the beginning of the topic where I had forgotten and neglected to take account of the radiator sizes I did know it. I think my disappointment was clouding my thinking.

Again, the monitoring and the help received from people here are invaluable.

For this I blame Octopus at the moment unless I find out other information to contradict my assessment when I will quite happily eat my words. I particularly blame the heat loss survey and the planning of the installation. I also blame the lack of setup assistance for which I also accept some blame as I thought I only really needed to set up a WD curve.

The installation itself is good and the price was good, although not really an influence for me, I would have had another installer if I could have found one.

However, despite the price, and I paid what I was I asked to pay, that does not give a company the right to install heating equipment that doesn’t work as it should.

I feel sorry for customers, of any installer, where they are not as engaged or knowledgeable enough to realise that something is wrong.

Those customers have been short changed and will probably never even know. They will just assume that’s how heat pumps are and in the worst cases damage the perceived suitability of heat pumps for homes in this country.

markocoheat · 26 October 2023 21:00

I should be writing a consultation response…but this is more interesting!

Fascinating that you’re not seeing any improvement dialling down temperatures. Fascinating that there’s such a descrepnacy in COP between Daikin units. Fascinating that they appear to share a single compressor across the range. Perhaps the midsize unit is the sweetspot for that range?

Can you draw an arrow on the photo that shows which way the water is flowing through the meter body?Can you show a photo of the meter body that has the flow direction arrow on it? It’s hopefully not considered a daft question!

These meters don’t flag any kid of error code if they’re reversed, or if they’re fully of much, as we learned on the OEM forum earlier this year. I’ve just had somebody swap one out for an ultrasonic unit elsewhere. COP 2.9 > 3.8 was the result. Quite the metering error. Unclear if backwards vs dirty at this stage. (I never saw it)

matt-drummer · 27 October 2023 07:13

Hi Marko,

The heat meter is installed on the return to the heat pump. There is nothing between it and the heat pump so it is measuring all of the water flowing through the heat pump. I have no leaks as my pressure is steady. The direction of flow is towards the camera.

Here is a photo of the arrow on the heat meter, it is installed in the correct orientation.

Here are pictures of my MMI controller showing energy consumed and heat produced.

Energy consumed

Heat produced

The OEM system is showing a better COP than the Daikin MMI is reporting. Energy consumption looks correct. Heat produced is quite different some days.

On Wednesday this week OEM reports 43 kWh of heat produced, Daikin shows something like 35 kWh

matt-drummer · 27 October 2023 07:32

Just thinking out loud.

In tests this heat pump was capable of a COP of 5.0 when it is 7c outside, flow temperature of 35c and a heat output of 5kW.

Installed at my house something needs to change to achieve this sort of COP?

It looks like the minimum electrical input is about 900w so I can never get a COP of 5.0 if my house only takes 3kW. I need the house to take about 4.5 kW to get the quoted performance.

Vinny · 27 October 2023 10:05

I wonder if the air purge process removes any air that might be at the top of the heat exchanger, the design seems to allow air to sit there. That would impede proper heat transfer, make one unit perform worse than the other.

matt-drummer · 27 October 2023 10:28

Hi Vinny.

My heat pump has a back up heater and an automatic air purge valve.